Topic
Magnetic lens
About: Magnetic lens is a research topic. Over the lifetime, 902 publications have been published within this topic receiving 7178 citations.
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Papers
TL;DR: Low energy electron microscopy (LEEM) is a surface imaging technique in which the surface is illuminated by an approximately parallel electron beam at near normal incidence as mentioned in this paper, and the image is formed with those electrons which are elas- tically backscattered into a small angular region around the surface normal.
Abstract: Low energy electron microscopy (LEEM) is a surface imaging technique in which the surface is illuminated by an approximately parallel electron beam at near normal incidence. The image is formed with those electrons which are elas- tically backscattered into a small angular region around the surface normal. The limitation to a small angular region is necessary because of the large aberrations of the objective lens which produces the primary image. This lens is a so-called cathode lens which not only has imaging properties but at the same time decelerates the fast electrons of the illuminating beam to the desired low energy at the specimen and re-accelerates the backscattered electrons to high energies again. In order to achieve this, the specimen is at a high negative potential which differs from the potential of the emitter of the electron gun of the illumination system by V 0 = E 0/e, where E 0 is the energy of the electrons at the specimen. Typical energy values are E = eV = 15−20 keV for the fast electrons and 0 < E 0 < 50 eV at the specimen. There are three fundamental quantities which are important in LEEM: resolution, intensity and contrast. These will be discussed in Sect. 12.1. Section 12.1 also describes how LEEM can be combined with other surface characterization techniques, such as low energy electron diffraction (LEED), photoemission electron microscopy (PEEM) and other emission microscopies. Section 12.2 illustrates the applications of LEEM and of the associated techniques to the study of clean surfaces, while Sect. 12.3 presents examples of the power of LEEM in the study of surface layers. Section 12.4 gives an outlook for possible future developments. A brief summary (Sect. 12.5) concludes this chapter.
676 citations
1 Aug 1937
TL;DR: In this article, the current density in a focused beam of cathode rays is shown to have an upper limit defined by I = I 0 (Ee/kT+1) sin2φ, where I is the maximum current density obtainable in the focused spot, E is the voltage at the focus relative to the cathode, T is the absolute temperature of the cathodes, e is the electronic charge, k is Boltzmann's constant, and φ is the half angle subtended by the cone of electrons which converge on the focused spots.
Abstract: The current density in a focused beam of cathode rays is shown to have an upper limit defined by I = I 0 (Ee/kT+1) sin2φ, where I is the maximum current density obtainable in the focused spot, I 0 is the current density at the cathode, E is the voltage at the focus relative to the cathode, T is the absolute temperature of the cathode, e is the electronic charge, k is Boltzmann's constant, and φ is the half angle subtended by the cone of electrons which converge on the focused spot. The cases in which the focused spot is an image of the cathode, and in which it is a pupil, or "crossover", are considered separately, and the above formula is shown to apply to both. The necessary initial assumptions are (1) that electrons leave the cathode with a Maxwellian distribution of velocities, and (2) that the focusing system is free from aberrations and obeys the law of sines. Aberrations may reduce the current density, but nothing can raise it above the value defined. In the Appendix the focusing properties of a uniform accelerating field are calculated. The virtual image of a plane cathode formed by such a field suffers from spherical aberration. The diameter of the circle of least confusion formed by electrons from a single point is approximately equal to the distance the electrons can travel against the field by virtue of their initial velocities.
141 citations
Patent•
30 Jan 1998TL;DR: In this article, a charged particle irradiation apparatus, which is capable of decreasing a lateral dose falloff at boundaries of irradiation field of charged particle beam and reducing the size of the charge particle irradiated apparatus, is provided by controlling magnetic fields of quadrupole electromagnets 1-5 and deflection electromagnetes 6-8 so that the center of the charged particle particle beam passes always center of a scatterer irrespective of direction and intensity of a magnetic field generated by scanning electromagnetic devices.
Abstract: A charged particle irradiation apparatus, which is capable of decreasing a lateral dose falloff at boundaries of irradiation field of charged particle beam, and reducing the size of the charged particle irradiation apparatus, is provided by controlling magnetic fields of quadrupole electromagnets 1-5 and deflection electromagnets 6-8 so that center of the charged particle beam passes always center of a scatterer irrespective of direction and intensity of a magnetic field generated by scanning electromagnets 50, 60.
116 citations
Patent•
2 Jul 1999
TL;DR: In this paper, an apparatus for examining a specimen with a beam of charged particles is described, where charging of the specimen is avoided or reduced by injecting inert gas onto the sample's surface.
Abstract: An apparatus for examining a specimen with a beam of charged particles, where charging of the specimen is avoided or reduced by injecting inert gas onto the sample's surface. In order to avoid interactions with the electron optics, various embodiments are disclosed for providing a rotationally symmetrical nozzles and/or electrodes. Additionally, embodiments are disclosed wherein a plurality of gas conduits are arranged in a rotationally symmetrical manner. Alternatively, the conduit is incorporated into an element of the electron optics, such as the magnetic lens. Also, in order to reduce or eliminate interaction of the electrons with the gas molecules, embodiments are disclosed wherein the gas is pulsated, rather than continually injected.
114 citations
TL;DR: In this article, the authors exploit the interactions in a quantum degenerate gas as an adjustable lens for coherent atom optics, where the focus is tuned by the strength of the lensing potential and the oscillatory phase of the quadrupole mode.
Abstract: In contrast to light, matter-wave optics of quantum gases deals with interactions even in free space and for ensembles comprising millions of atoms. We exploit these interactions in a quantum degenerate gas as an adjustable lens for coherent atom optics. By combining an interaction-driven quadrupole-mode excitation of a Bose-Einstein condensate (BEC) with a magnetic lens, we form a time-domain matter-wave lens system. The focus is tuned by the strength of the lensing potential and the oscillatory phase of the quadrupole mode. By placing the focus at infinity, we lower the total internal kinetic energy of a BEC comprising 101(37) thousand atoms in three dimensions to 3/2 kB⋅38+6−7 pK. Our method paves the way for free-fall experiments lasting ten or more seconds as envisioned for tests of fundamental physics and high-precision BEC interferometry, as well as opens up a new kinetic energy regime.
81 citations
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Performance Metrics
| Year | Papers |
|---|---|
| 2025 | 3 |
| 2024 | 1 |
| 2023 | 4 |
| 2022 | 12 |
| 2021 | 10 |
| 2020 | 25 |